GENERATOR PKG ERECTION PART-II, LIFTING ARRANGEMENTS OF GENERATOR - ABC OF THERMAL POWER PLANT.

PART- II

Stator lifting by EOT Cranes:-

In earlier days up to 210 /250 MW class the stator is being lifted by two EOT cranes of similar capacity  with lifting beam. EOT cranes main hooks are fitted with the lifting beam and lifting beam main hook is being utilised for lifting stator by using special sling designed for the above purpose. Stator  is placed in the service bay within the approach of EOT crane and unloaded from Trailer / wagon as the transportation method available in the power house. Earlier days a railway line runs  across the service bay. Now a day’s all the stator is coming by high capacity hydraulic Trailer.  Stator is unloaded by hydraulic jacks on temporary supports in the service bay. Fix the trunion plates (04 nos) with the body of the stator after necessary cleaning and blue matching with stator body. This has to be fixed as per the norms because sling will be placed on it. Clean the terminal box and do the blue matching with surface plate. This are the preparatory work for stator lifting. Terminal Box can be placed before stator if there is no other possibilities push it from bottom. Stator is lifted by tandem operation with lifting beam from any of one the crane. This arrangements to be tested before put in actual use. Necessary adjustment to be carried at that time, to avoid any jerk during the operation.

Stator lifting by Portal crane or by strand jack method.:-

Once we are start erecting 500 MW /600 MW /660 MW /800 MW generators the weight of the stator

increases considerable therefore alternative lifting arrangements are thought of . Some of the

utilities  think about the lifting irrespective of loading TG  bay . Otherwise total TG bay need to designed taking stator weight as one of the factor.  Portal crane and strand jack method came as solution. It has been seen availability of Portal is a problem. In my service life we have noticed  that once we need to erect 09 numbers of stator in a year and we have only two portal cranes. Portal dismantling , transportation and re –erecting is 03 to 04 months cycle depends on location of both the sites . We cannot erect all the Generators required by management and to solve this problem stand jack method of stator lifting was adopted. This type of lifting was already popular for boiler drum lifting.

Placement of stator for this type of lifting is very important. The stator need to be placed outside A row column and between transformer bay and A row column. Centre line  of  Generator from TG to be brought and marked for stator placement . No axial movement is possible when stator is placed on foundation. Foundation for jack pads and lifting structures are needed for unloading  the generator  and placed on temporary supports. All other works to be done on generator is same. Stand jack system to be erected by EOT crane and Heavy lift Crawler crane from AB bay and Outside A row. Close co –ordination is required from all quarters as that area includes the area of CW pipelines  for Condenser. Clear approaches is required for heavy duty crane and Hydra cranes.

As the main column pitch distance is less than the stator length swivel arrangement is required in strand jack system. Strand jack system is totally hydraulic and operates slowly it may take  06 to 08 hrs from start to complete the lifting and placement  operation.

Continued to Part -III for more pictorial representation.P.S If  you are looking to earn few extra money from the comfort of your home then please click on the link given below

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GENERATOR PKG ERECTION PART-I, GENERAL FEATURES OF GENERATOR WITH PHOTOES - ABC OF THERMAL POWER PLANT.

PART -I

Generator with exciter is the ultimate  output of all the system put together. This is very important item to be installed with turbine system. Generator is the heaviest item to be installed in the power house in single lift. In earlier days generators ( up to 300 MW) class were installed by two EOT crane by using common hook  and tandem operation. But 500 MW onwards this practice was discarded because the structural design and cost required to be done is much higher than the conventional one. Therefore a method was involved to lift the generator which has no bearing with the structural load bearing capacity. Use of Portal crane and more popular is strand jack method gained popularity for lifting stator . We will discuss the same with photographs on later dates. A brief description of 500 MW generator  is given below for new comers.

The two-pole generator uses direct water cooling for the stator winding, phase connectors and bushings and direct hydrogen cooling for the rotor winding. The generator frame is pressure-resistant and gas tight and equipped with one stator end shield on each side. The hydrogen coolers are arranged vertically inside the turbine end stator end shield.

The generator consists of the following components:

• Stator

Stator frame ,End shields ,Stator core ,Stator winding and Hydrogen coolers.

• Rotor

Rotor shaft , Rotor winding, Rotor retaining rings and Field connections

• Bearings

Shaft seals

The following additional auxiliaries are required for Generator operation :

• Oil system , Gas system , Primary water system and  Excitation system.

Cooling System.

-The heat losses arising in the generator interior are dissipated to the secondary coolant (raw water,

condensate etc.) through hydrogen and primary water.

-The hydrogen is circulated in the generator interior in a closed circuit by one multi-stage axial-flow fan arranged  on the rotor at the turbine end. Hot gas is drawn by the fan from the air gap and delivered to the coolers, where it is re-cooled and then divided into three flow paths after each cooler.

-For direct cooling of the rotor winding, cold gas is directed to the rotor end windings at the turbine and exciter ends. The rotor winding is symmetrical relative to the generator centre line and pole axis. Each coil quarter is divided into two cooling zones.

For cooling of the stator core, cold gas is admitted to the individual frame compartments via separate cooling gas ducts. From these frame compartments the gas then flows into the air gap through slots in the core where it absorbs the heat from the core.

The treated water used for cooling of the stator winding phase connectors and bushings is designated as primary water in order to distinguish it from the secondary coolant (raw water, condensate, etc.). The primary water is circulated in a closed circuit and dissipates water is circulated in a closed circuit and dissipates the absorbed heat to the secondary cooling water in the primary water cooler. The pump is supplied with hot primary water from the primary water tank and delivers the water to the generator via the coolers. The cooled water flow is divided into two flow paths .

Stator Frame

 The stator frame consists of a cylindrical centre section and two end shields which are gas-tight and pressure-resistant. The stator end shields are joined and sealed to the stator frame with an O-ring and bolted flange connection. The stator frame accommodates the electricity active parts of the stator, i.e., the stator core and the stator windings.

The stator core is stacked from insulated electrical sheet-steel laminations and mounted in supporting rings over insulated dovetailed guide bars. Axial compression of the stator core is obtained by clamping fingers, pressure plates, and non-magnetic through-type clamping bolts, which are insulated from the core.

The rotor shaft is a single-piece solid forging manufactured from a vacuum casting. Slots for insertion of the field winding are milled into the rotor body. The longitudinal slots poles are obtained. The rotor poles are designed with transverse slots to reduce twice system frequency rotor vibrations caused by deflections in the direction of the pole and neutral axis.

The hydrogen cooler is a shell and tube type heat exchanger which cools the hydrogen gas in the generator. The heat removed from the hydrogen is dissipated through the cooling water. The cooling water flows through the tubes, while the hydrogen is passed around the finned tubes.

The sleeve bearings are provided with hydraulic shaft lift oil during start-up and turning gear operation. To eliminate shaft currents, all bearings are insulated from the stator and base plate, respectively. The temperature of the bearings is monitored with thermocouples embedded in the lower bearing sleeve so that the measuring points are located directly below the BABBITT. Measurement and any required recording of the temperatures are performed in conjunction with the turbine supervision. The bearings have provisions for fitting vibration pickups to monitor bearing vibrations.

Typical 500MW Generator Specification

KW 500,000 ; KVA 588,000 Hz 50 ; R.P.M 3000 ; P.F. 0.85 LAG

Stator  : Volts 21000 ;  Amps 16200 ;  Phase 3; Conn. Y Y ;  Spec. IEC-34

Rotor  :  Amps 4040 ; Volts 340  : Coolant Hydrogen & Water; Gas Pressure 3.5 Kg/cm2 (g)

         Typical 500MW Generator cross section

 Typical 500MW Generator outline drawing and 660 MW  generator. Difference of construction

will be outlined later.

courtesy  BHEL

Continued to PART -II

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